EXTRACTION OF SEDIMENTS FOR AROMATIC AND CHLORINATED HYDROCARBONS

Transcription

1 EXTRACTION OF SEDIMENTS FOR AROMATIC AND CHLORINATED HYDROCARBONS Juan. A. Ramirez, Bo Wang, Donell S. Frank, Thomas. J. McDonald, Rebecca Price, Susanne J. McDonald and James M. Brooks TDI-Brooks International./B&B Laboratories Inc. College Station, Texas ABSTRACT Determining organic contaminant levels in sediments requires extraction, isolation and concentration from the matrix. Sediment samples are dried, powdered and homogenized prior to extraction. Sediments are extracted in dichloromethane using a Dionex ASE200 Accelerated Solvent Extractor. The extracts are concentrated and then purified using alumina/silica gel chromatography columns. The resultant eluent is concentrated to a final volume of 1.0 ml and submitted for the determination of aromatic and chlorinated hydrocarbons by gas chromatography/mass spectrometry and gas chromatography/electron capture detection. 1.0 INTRODUCTION The procedure described is capable of extracting, isolating, purifying and concentrating aromatic and chlorinated hydrocarbon contaminants at the parts per billion or parts per trillion level in sediments. Sediment samples are thawed and homogenized. An aliquot of 1-2 g is removed for percent moisture determination. Another aliquot is oven dried at 40 C prior to extraction. Once samples are dried they are ground and homogenized using a mortar and pestle. Approximately 15 g of dry sediment is extracted with 100% dichloromethane using a Dionex ASE200 Accelerated Solvent Extractor operated at 100 C and 2,000 psi. The extracts are concentrated to 1 ml by evaporative solvent reduction in a C water bath. The concentrated sediment extract is purified using alumina/silica gel column chromatography. The extracts are once again concentrated to 1 ml and submitted for instrumental analysis. 2.0 APPARATUS AND MATERIALS 2.1 EQUIPMENT Dionex, ASE200 Accelerated Solvent Extractor (ASE) with 33 ml extraction cells Sediment Extraction for Hydrocarbons - 1

2 Water bath, capable of maintaining a temperature of C Balance, top loading, tare capacity to 300 g, capable of weighing to 1 mg Microbalance, capable of weight to 1 µg Calibrated weights, certified Combustion furnace, electric capable of combusting glassware at 400 C for at least 4 hours Oven, capable of 40 C temperature maintenance Conditioning oven, electric, gravity convection, capable of maintaining a stable temperature of up to 200 C Tumbler, Lortone rock tumbler or equivalent Collection vials, 60 ml certified pre-cleaned with open screw caps and Teflon lined VOA septa Micropipettors, calibrated, 1% accuracy, disposable tips 250 ml flat bottom, boiling flasks Borosilicate glass chromatography columns, 300 mm x 19 mm, with Teflon stopcock Kurderna-Danish (K-D tubes), 25 ml, slow dry concentrator tubes Synder columns, 3 ball Boiling chips, Teflon Glass wool 2.2 REAGENTS Water, gas chromatography/hplc grade or equivalent purity Acetone, pesticide grade or equivalent purity Dichloromethane, pesticide grade or equivalent Hexane, pesticide grade or equivalent Pentane, pesticide grade or equivalent Copper, granular, purified with hydrochloric acid Hydrochloric acid Sodium sulfate, purified by combusting at 400 C for at least 4 hours and stored at 120 C. Alumina, mesh, basic, purified by combusting at 400 C for at least 4 hours and stored at 120 C Silica gel, grade 923, mesh, purified in an oven at 170 C for at least 16 hours and store at 170 C Nitrogen, 99.8% purity 3.0 PROCEDURE All glassware used to extract sediments is washed, solvent rinsed or combusted at 400 C for at least 4 hour. All other items that come in contact with samples are washed and solvent rinsed with acetone and dichloromethane. Sediment samples are thawed and Sediment Extraction for Hydrocarbons - 2

3 homogenized. A portion (1-2 g) is removed for percent moisture determination (see Dry Weight Determination of Sediments). Samples are dried in an oven at 40 C and then ground and homogenized using a motar and pestle. Approximately 15 g of the dried sediment is extracted. Sediments are extracted with dichloromethane using an ASE200. Dried samples are loaded into 33 ml stainless steel ASE extraction cells. Appropriate surrogate and spikes are added on top of the samples. Quality control samples (e.g., blanks, duplicates, matrix spikes and standard reference materials) are prepared in the same manner as samples. The ASE extractor tubes are sealed and placed on the ASE cell carousel. The ASE conditions are 100% dichloromethane as the extraction solvent, 2,000-psi solvent pressure, 100 C cell temperature, and 2 static cycles for 2 minutes each. Extracts are collected in 60 ml collection vials. The extracts are concentrated to approximately 10 ml in the 60 ml collection vials in a C water bath. Extracts are then quantitatively transferred to Kurderna-Danish (K-D) tubes and concentrated to 1.0 ml in a C water bath. Extracts are purified using alumina/silica gel chromatography columns. Borosilicate glass columns (300 mm x 19 mm) are packed with conditioned sodium sulfate, alumina and silica gel. Combusted and cooled alumina is deactivated by adding 1% (w/w) reagent water and tumbled for at least 1 hour using a Lortone rock tumbler. Combusted, cooled silica gel is deactivated by adding 5% (w/w) reagent water and tumbled for at least 1 hour using a Lortone rock tumbler. The columns are packed in dichloromethane with glass wool, 1-2 g of cooled sodium sulfate, 10 g of deactivated alumina, 20 g of deactivated silica gel and another 1-2 g of sodium sulfate. The dichloromethane is drained to the top of the column and replaced with 50 ml of pentane. The pentane is drained to the top of the upper sodium sulfate layer and discarded. The sample extract (approximately 1 ml) is loaded on top of the column and flushed with 200 ml of a 50:50 mixture of pentane and dichloromethane at a flow rate of 1 ml/min. The eluent is collected in a 250 ml flatbottom flask. The eluent is concentrated to approximately 10 ml in a C water bath. The extract is transferred to 25 ml K-D tubes and concentrated. The dichloromethane is exchanged to hexane and concentrated to a final volume of 1 ml. The concentrate is transferred to 2 ml amber vials containing pre-cleaned copper granules and stored at 20 C until analysis. High sulfur containing samples may require additional copper treatment. Figure 1 shows a flow chart of the extraction and purification procedure. Sediment Extraction for Hydrocarbons - 3

4 SAMPLE RECEIPT AND STORAGE SAMPLE PREPARATION % MOISTURE DETERMINATION SAMPLE EXTRACTION SAMPLE CLEANUP VIA ALUMINA/SILICA GEL COLUMN EXCHANGE DICHLOROMETHANE TO HEXANE ANALYSIS BY GC/MS (PAHS) ANALYSIS BY GC/ECD (OCS) Figure 1. Methodology for Extraction, Isolation and Quantification of Sediment Samples for Aromatic and Chlorinated Hydrocarbons. Sediment Extraction for Hydrocarbons - 4

5 4.0 QUALITY CONTROL (QC) All reagents used are verified to be contaminant free. All equipment and glassware used to extract samples are thoroughly cleaned by solvent rinsing or combustion at 400 C. The calibration and accuracy of balances, weights, pipettors and thermometers are checked daily. The calibration and accuracy of balances, weight, pipettors and thermometers are verified yearly by an independent source. All samples are shipped and received under chain-of-custody. A series of quality control samples are processed with each batch of 20 samples or less. The following quality controls are used to ensure the accuracy and precision of sediment data. Surrogates. Solutions containing analytes that do not interfere with the analytes of interest are prepared at concentrations approximately 5 to 10 times the method detection limit (MDL). Specified surrogates are added to each sample extracted, including QC samples, at a specified volume (typically 100 µl) immediately prior to extraction. Method Blank. Method blanks are extractions of all support material used for extraction of samples, with the exception of sediment. A method blank is analyzed with each extraction batch of 20 or fewer samples. The method blank is extracted and analyzed in a manner identical to samples. Matrix Spike. Matrix spikes are extractions of sample matrix fortified with spikes of selected target analytes. A matrix spike and matrix spike duplicate are analyzed with each extraction batch of 20 or fewer samples. Matrix spikes are extracted and analyzed in a manner identical to samples. Laboratory Duplicates. A sample is analyzed in duplicate with each extraction batch of 20 or fewer samples. Standard Reference Material. A standard reference material from the National Institute of Standards and Technology (NIST) is analyzed with each extraction batch of 20 or fewer samples. Sediment Extraction for Hydrocarbons - 5